code: def _build_evaluation(self):
      self.metrics = {"BLEU": BLEU(n_grams=[1, 2, 3, 4])}
  
imports: import os
  import resource
  import numpy
  import torch
  import torch.optim
  from torch.utils.data import DataLoader
  from torch.utils.tensorboard import SummaryWriter
  from graph4nlp.pytorch.models.graph2seq import Graph2Seq
  from graph4nlp.pytorch.models.graph2seq_loss import Graph2SeqLoss
  from graph4nlp.pytorch.modules.evaluation import BLEU
  from args import get_args
  from build_model import get_model
  from dataset import IWSLT14Dataset
  from utils import WarmupCosineSchedule, get_log, wordid2str
label_desc: Use image node_id 7 for calling the NMT obj's underlying member method code with example usage: obj._build_evaluation() without return types